The invention relates to a device for ventilation via an endotracheal tube.
The predominant majority of patients being ventilated during an intensive-care therapy or anaesthesia have their airway secured by an endotracheal tube. To this end, an endotracheal tube which consists of a plastic or rubber tube, as a rule, is introduced into the trachea through the mouth or nose or by a making an incision in the trachea (“tracheotomy”). At the tracheal end, the endotracheal tube mostly is provided with a inflatable endotracheal tube “cuff” which seals the trachea, permits ventilation at an excess pressure, and protects the airways from the penetration of foreign matter. The end distal to the patient of the endotracheal tube is coupled to a ventilation device via a hose system. At the point of transition from the endotracheal tube to the hose system, there is an Y connection piece which has connected thereto an inspiratory hose and an expiratory hose or expiratory valve leading to the atmosphere.
A respiratory air filter can be disposed between the endotracheal tube and the hose system to minimize the exchange of micro-organisms and other contaminants between the patient and hose system. The extension of time intervals between the exchanges of the hose which becomes possible thereby is advantageous both economically and ecologically. Further, heat-and-moisture exchangers may be provided between the hose system and the endotracheal tube which cause the inspiration air to be humidified to prevent the patient's airways from becoming parched. This is accomplished by condensing the moisture contained in the expiration air on specific filter-like materials and re-evaporating the moisture during the succeeding inspiration. Further, there is a so-called “active humidification” via a heated evaporator in the inspiratory hose of the hose system.
The lungs effect an exchange of gas with the external air in a pendular process. At this stage, whenever an inspiration takes place gas which has been left behind from prior expiration in the so-called “dead space” first gets into the lungs. The dead space is the entirety of all air conductors which are flowed through during both inspiration and expiration. It comprises the bronchi and trachea as well as the conventionally single-lumen endotracheal tube and any preceding breathing air filters or heat-to-moisture exchangers. It ends in an Y-connector which ramifies the airway for inspiration and expiration.
The respiratory excursions subject the lungs to mechanical loads and require the spontaneously breathing patient to do breathing effort. Since the dead space (both anatomical and device-related) can constitute a significant percentage of the respiratory stroke (about 30% to more than 50%) its minimization is an important step towards reducing such loads and breathing effort fractions. A known action to reduce the dead space is to insert an endotracheal tube having two lumina (a “double-lumen endotracheal tube”) which are separately connected to the inspiratory hose and expiratory hose or the expiratory valve leading to the atmosphere. A ventilation system having a double-lumen endotracheal tube is described in DE 25 35 191 A1, for example. In a double-lumen endotracheal tube, a separator for the inspiration and expiration legs of the ventilation device is installed in lieu of a connection piece for the two lumina. It is located deeply in the trachea at the tracheal end of the endotracheal tube. Accordingly, this reduces the dead space of the system and the breathing effort which caused by the dead space.
Another advantage of double-lumen endotracheal tubes is provided when there is a pressure-regulating ventilation. During such a ventilation, the ventilator aims at regulating the pressure at the Y connection piece. To this end, the common ventilators do not carry out a pressure tap which is separately led up to the Y connection piece because the pressure prevailing there can be measured just as well via the upright gas column of the hose which is just not flowed through during the respective respiratory phase. When a double-lumen endotracheal tube is used the Y connection piece and, hence, the regulation point will be shifted into the trachea. As a direct consequence, the patient need no longer overcome that part of breathing effort which is caused by the flow resistances in a single-lumen endotracheal tube. The task of overcoming the flow resistances of the double-lumen endotracheal tube is automatically imposed on the ventilator.
When the endotracheal tube kinks or foreign matter such as secretions from the trachea settle(s) in its interior its resistance will increase. This can cause a hazard to the patient because it will impede its ventilation and/or high pressures will build up in the lungs (with restriction being preponderant to expiration). Since such changes occur to the portion of the endotracheal tube that cannot be seen in a visual inspection only late signs will be noticed, i.e. reductions to ventilation or pressure rises.
These disadvantages can be overcome to a limited extent by monitoring the pressure at the Y connection piece and the gas flows. However, such monitoring cannot discriminate or associate the mechanical properties of the structures beyond the Y connection piece (filter, endotracheal tube, airways, lungs, surrounding tissue, muscle activity). Therefore, monitoring the tube properties is only possible to a very limited extent and only major changes are detected, if at all.
Another problem is posed by the necessity for constant humidification of the patient's inspiration air because the endotracheal tube keeps it away from the natural humidifiers (the mucosae of the nose and pharynx). Heat-and-moisture exchangers, as a rule, simultaneously function as filters, thus forming a contaminant barrier between the patient and the hose system. However, they require to be alternately flowed through by expiration and inspiration air to satisfy their function. Therefore, they cannot be employed for double-lumen endotracheal tubes. At present, if double-lumen endotracheal tubes are used it is only possible to actively humidify such air by means of electrically heated evaporators.
Another problem is how to remove secretions and foreign matter from the endotracheal tube. While a ventilation therapy is performed the natural cleaning mechanism of the airways is capable of transporting secretions and foreign matter into the trachea up to the endotracheal tube, if at all. They have to be drawn off not later than from this point. To this end, it is usual to disconnect the Y connection piece from the endotracheal tube so permit a suction catheter to be introduced into the endotracheal tube. This interrupts ventilation and any continuously positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP), which is a common prophylaxis against the collapse of diseased parts of the lung, cannot be maintained. Therefore, special inflation manoeuvres become necessary after this suction to re-open collapsed parts of the lungs.
Furthermore, it has been known already to introduce the suction catheter through a particular angled adapter, which forms a seal around the catheter, between the endotracheal tube and the Y connection piece. The ventilator remains connected to the endotracheal tube and ventilation can be continued, on a principle. However, problems will arise by the fact that the portion of the lumen that is responsible for ventilation is reduced in dependence on the dimensions of the endotracheal tube and suction catheter and, as a consequence, its resistance to both inspiration and expiration air is more or less increased. Recent studies have shown that continuing a volume-controlled ventilation should be avoided in any case under these circumstances: Hazardous positive or negative pressures are possible, which depend on the pattern of ventilation and the different dimensions of the hose. Therefore, if ventilation is to be continued under a suction this has definitely to be done in a pressure-regulated mode. Even then, if a conventional single-lumen endotracheal tube is used the pressure in the trachea will always be distinctly below the target pressure setting during a suction because there is the endotracheal tube with its reduced lumen between the trachea and the Y connection piece, the point of measurement and regulation.
DE 195 28 113 A discloses a ventilation device for the controlled mechanical ventilation of patients including a measurement and evaluation of the expiratory time constant of the respiratory system. Characteristic changes of the time constant-to-volume relationship are supposed to allow the detection and differentiation of elevated resistances or obstructions of the endotracheal tube, on one hand, and those of the trachea and bronchi, on the other.
GB 2 318 518 discloses a double-lumen endotracheal tube in which one lumen serves for the supply of a continuous flow of fresh gas and the larger lumen serves for discontinuous expiration. Controlled ventilation is effected by a phased closure of the larger lumen. The expiration limb of the device has connected thereto a pressure sensor.
U.S. Pat. No. 3,102,537 A discloses a respiration device with a face mask, particularly for air and space travel, which ensures improved transfer of moisture from the expired air to the inspired air and a maximum saving of oxygen or another inspired gas from an external source. A common wall permeable to moisture is disposed between the expiration and the inspiration air conduit. In addition, there is a reservoir which is passed in by a first portion of the expired gas in order to be inspired first during the following inspiration.